recovery of plant species richness and composition after slash

ORI GIN AL PA PER

Recovery of plant species richness and compositionafter slash-and-burn agriculture in a tropicalrainforest in Madagascar

Kari Klanderud • Hery Zo Hasiniaina Mbolatiana •

Manjato Nadiah Vololomboahangy • Marie Agnes Radimbison •

Edmond Roger • Ørjan Totland • Charlotte Rajeriarison

Received: 4 February 2009 / Accepted: 22 September 2009 / Published online: 9 October 2009� Springer Science+Business Media B.V. 2009

Abstract Slash-and-burn agriculture is an important driver of deforestation and eco-

system degradation, with large effects on biodiversity and carbon sequestration. This study

was conducted in a forest in Madagascar, which consists of fragments of slash-and-burn

patches, within a matrix of secondary and primary forest. By recording species richness,

abundance, and composition of trees, shrubs, and herbs in fallows of various age and slash-

and-burn history, and in the secondary and primary forest, we show how slash-and-burn

intensity (number of cycles, duration of abandonment), years since last abandonment, and

environmental factors (distance to primary forest and topography) affect the natural suc-

cession and recovery of the forest ecosystem. We used ordination analyses to examine how

the species composition varied between the different successions stages, and to examine

tree recruitment. Our results show shrub dominance the first years after abandonment.

Thereafter, a subsequent increase in species richness and abundance of tree seedlings and

saplings suggests a succession towards the diversity and composition of the secondary and

primary forest, although a big gap between the oldest fallows and the secondary forest

shows that this will take much more than 30 years. A high number and frequency of slash-

and-burn cycles decreased tree seedling and sapling richness and abundance, suggesting

that reducing slash-and-burn intensity will increase the speed of tree recruitment and

fallow recovery. Trees can be planted into fallows to speed up vegetation and soil recovery,

such that fallows can be usable within needed time and thus the extension of cultivated

areas reduced. We recommend further testing of six potential species for restoration based

on their early colonization of the fallows and their survival through vegetation succession.

K. Klanderud (&) � Ø. TotlandDepartment of Ecology and Natural Resource Management, Norwegian Universityof Life Sciences, P.O. Box 5003, 1432 As, Norwaye-mail: [email protected]

K. KlanderudDepartment of Biology, University of Bergen, Bergen, Norway

H. Z. H. Mbolatiana � M. N. Vololomboahangy � M. A. Radimbison �E. Roger � C. RajeriarisonDepartment of Biology and Vegetation Ecology, Faculty of Science,University of Antananarivo, BP 906 Antananarivo, Madagascar

123

Biodivers Conserv (2010) 19:187–204DOI 10.1007/s10531-009-9714-3

Keywords Biodiversity conservation � Forest degradation � Land use �Recruitment � Restoration � Tropical forest � Vegetation succession

Introduction

The global loss of forested areas is considered one of the largest threat to humanity, not

only due to the loss of biodiversity in forests, but also due to the reduced amount of

sequestrated carbon (Houghton et al. 2000; Grace 2004). Slash-and-burn agriculture is one

of the main drivers of deforestation and subsequent land degradation, and is currently

practiced by ca. 300–500 million people to provide food and an occasional small amount

of income from cash crops (Brady 1996). Slash-and-burn agriculture initially involves the

cutting of forest followed by burning of the plant material. Thereafter slashed and burned

areas are subjected to a cycle of cultivation and abandonment. The duration of each cycle

period depends on factors such as soil fertility, the crop type, the availability of crop areas,

and population growth (Smith et al. 1999; Styger et al. 2007). Due to the low nutrient

content of tropical soils, slash-and-burn, like other farming systems not using fertilizer, is a

low-yield agriculture system. Coupled with increased human population size, particularly

in the tropics, that cause increased demands of food, people are broadly left with two

options. Either they start to use fallow areas after a shorter period of soil recovery (during

which nutrient content builds up) (Dalle and de Blois 2006), or they extend the area of

cultivation into primary or secondary forests (Gehring et al. 2005; Styger et al. 2007). At

both global and local levels, this results in a loss of forested areas, causing decreased

amounts of sequestrated carbon that could mitigate anthropogenic emissions of CO2

(Houghton et al. 2000) and result in a potential loss of biodiversity (e.g. Sala et al. 2000).

In Madagascar, containing unique, and one of the richest floras and faunas of the world

(Myers et al. 2000), slash-and-burn agriculture has been attributed the main cause of

primary forest fragmentation and loss, and soil degradation, during the last 150 years (e.g.

Oxby and Boerboom 1985; Gade 1996; Marcus 2001). In Madagascar, as elsewhere, fallow

periods are shortened, primarily due to lack of, or not readily adopted, alternative incomes

and food types, and because of increased population growth (Styger et al. 2007). Both

nationally (Madagascar Action Plan 2007–2012) and internationally (e.g. Green and

Sussman 1990; Myers et al. 2000) there is a growing concern about the accelerating loss of

forests in Madagascar, and knowledge that could contribute to reduce or stop primary

forest loss and halt further fragmentation of existing forest areas is apparently still needed.

In this work, we study the effects of slash-and-burn agriculture on plant species rich-

ness, abundance, and composition, and the natural succession and recovery of plant

communities after disturbance. Our study was conducted in the Vohimana forest fragment,

situated between the three larger primary evergreen forests Mantadia National Park,

Analamazaotra, and Maromizaha, towards the eastern coast of Madagascar. The position of

the Vohimana forest, as a small isolated forest patch between the larger forests, is

potentially important for forming a forest corridor that could connect these larger primary

forest areas. Man and the environment (MATE http://www.madagascar-environnement.

com/) has been involved in the conservation of Vohimana since 2003, and several studies

have documented large negative effects of slash-and-burn agriculture on the faunistic and

floristic diversity in the area (e.g. Rabemananjara et al. 2003; Randrianirina 2005).

Vegetation succession after abandonment of slash-and-burn areas has also been studied in

other areas of Madagascar (Lowry et al. 1997; Styger et al. 2007), South America (e.g. Uhl

188 Biodivers Conserv (2010) 19:187–204

123

http://www.madagascar-environnement.com/

http://www.madagascar-environnement.com/

1987; Miller and Kauffman 1998; Smith et al. 1999; Gehring et al. 2005), and in South

East Asia (e.g. Roder et al. 1997). However, little knowledge exists on how variation in

slash-and-burn intensity and the colonisation of primary and secondary forest species into

fallows, affect the speed and direction of natural succession and the recovery of the forest

ecosystem (but see Guariguata and Ostertag 2001; Dalle and Bois 2006; Styger et al.

2007). Slash-and-burn agriculture can be seen as a series of disturbances, where each stage

(cutting, burning, weeding) have dramatic effects on the mortality and regeneration of

plant species (Uhl 1987). Moreover, the combined effect of each of these stages may

reduce or eliminate the potential for on-site tree regeneration, leaving seed dispersal as the

major way for establishment of species from the nearby primary forest. A key factor of

fallow succession is the re-establishment of forest species, which can be a slow process

(e.g. Uhl 1987; Guariguata and Ostertag 2001; Brearley et al. 2004), although some spe-

cies, in particular those adapted to colonizing forest gaps, may establish fast. Studies have

shown that planting of trees, or single remnant trees, such as for example fruit trees, and

logs, may facilitate tree regeneration through shading of the seedlings (Uhl 1987) or by

nucleation due to the attraction of seed dispersers (Guariguata and Ostertag 2001; Carriere

et al. 2002). On the other hand, dense canopies of pioneer shrubs that invade fallows are

predicted to inhibit the growth of tree seedlings (Styger et al. 2007), although this may be

species dependent, as some may even facilitate the establishment of trees. Indeed, more

knowledge is needed to understand the relationship between early colonizers and fallow

succession. By obtaining detailed information on the intensity of use (number of slash-and-

burn cycles and average fallow duration), time since last abandonment of slash-and-burn

fallows, and the species richness and composition of fallows and secondary and primary

forest, we aim to answer the following questions: (1) how do species richness and the

abundance of trees (seedlings, saplings, adults), shrubs, and herbs develop after aban-

donment of slash-and-burn areas, (2) how does slash-and-burn intensity affect vegetation

succession and recovery of fallows, (3) how do distance to the primary forest, altitude, and

slope affect the vegetation succession and recovery of fallows, and (4) based on our results;

which local species may be suitable candidates in an active restoration programme of the

degraded forest areas in the study area?

Materials and methods

Study area

Vohimana forest (18�540–18�560S, 48�280–48�310E) is situated at ca. 700–1000 m eleva-

tion ca. 150 km east of Antananarivo, Madagascar’s capital city, and ca. 6 km north of the

village Ambavaniasy. The climate is hot and humid, highly influenced by moist winds

from the east, and with no dry season. Average annual precipitation is 1850 mm and

average annual temperature is 20.4�C. The Vohimana area consists of a patchwork of

fallows of various ages in a matrix of secondary and primary forest patches of different

sizes. The natural forest is a wet and dense evergreen forest (Randrianirina 2005). Areas

below ca 800 m altitude belong to the floristic zone characterized by Anthostema and

Myristicaceae tree species, whereas areas above ca 800 m altitude are characterised by

Weinmannia and Tambourissa tree species (Faramalala and Rajeriarison 1999). What we

define as secondary forest in this study is an intact forest disturbed by selective harvesting,

tree cutting and/or uncontrolled fire. The fallows are dominated by herbs (e.g. Asteraceae,

Poaceae) and shrubs (e.g. the native Psiadia altissima and the introduced invasives

Biodivers Conserv (2010) 19:187–204 189

123

Lantana camara and Rubus mollucanus) and have only a few single trees (the introduced

Trema orientalis and the native Croton mongue).

Field methods

We selected 33 slash-and-burn areas where we had reliable information on the start of the

slash-and-burn period, the number of slash-and-burn cycles, and the number of years since

the last abandonment. This information was obtained by interviewing people using the area

and a local guide. Our sample of fallows represents the current variation of fallow duration

in the Vohimana area, with the oldest plots started being used for slash-and-burn in 1930,

and with a range from 1 to 26 years since the last exploitation. In addition, we randomly

selected 12 plots in secondary and 6 in primary forest in order to compare species richness,

abundance, and composition in fallows with that of secondary and primary forest plots. In

fallows and secondary forest, 5 9 30 m plots were positioned in the centre of the fallow or

forest patch. Each plot consisted of six 5 9 5 m sub-plots and each sub-plot had a 1 9 1 m

quadrat in its centre. We measured the diameter at breast height of each plant taller than

1.3 m (dbh) at 1.3 m height with a dbh-meter. For trees and shrubs with a dbh of[10 cm,

we counted the individuals of all species within each of the six sub-plots. Individuals with

dbh \ 10 cm and height[1 m were counted and determined as far as possible to species or

genus in every second sub-plot. We estimated the abundance of all plants \1 m by

recording the percentage cover within each of the 1 9 1 m quadrats. Trees with

dbh [ 10 cm were defined as adults, trees with dbh \ 10 cm and height [1.3 m were

defined as saplings, and trees \1.3 m height were defined as seedlings. In the primary

forest we used 15 9 30 m plots, divided into three 5 9 30 m plots and 18 sub-plots to

estimate species richness, abundance, and composition. We used a larger plot size here in

order to capture the variation in the tree species composition. Apart from the difference

in plot size, the methodology of obtaining data on the presence and abundance of species in

the primary forest was as described above. To correct for the three times larger plot size in

the primary forest, species counts (abundance) for each large plot were divided by three

before data analyses. For species richness, we calculated the number of species for each of

the three 5 9 30 m plots separately and used the mean. Plots in the primary forest were

positioned at least 100 m away from the forest edge towards fallow or secondary forests to

avoid any edge effects. For each plot in fallows we estimated the distance to the closest

part of the primary forest. For all plots, we measured the altitude and the coordinates with a

GPS, the slope with a clinometer, and the exposition with a compass.

Statistical analyses

The fallows were divided into 4 age categories, depending on the number of years since the

last abandonment (1: 1–3 years; 2: 4–7 years; 3: 8–12 years; 4: 13–26 years). Secondary

and primary forests were set as age class 5 and 6, respectively. We used one-way ANOVAs

to examine if total species richness (all species), and species richness and abundance of

herbs, shrubs, tree seedlings, tree saplings, and adult trees (dependent variables) differed

among age classes (fixed variable). We used the Tukey‘s HSD post-hoc test to examine if

response variables differed significantly between individual age classes.

Due to the Poisson distributions observed in the dependent variables in the fallows, we

used Generalized Linear Model multiple regressions with a log link function to examine

the relative importance of the different environmental variables for species richness and


123

abundances there. The environmental variables used were (a) linear distance from the

fallow to the primary forest, (b) slope of the fallow, (c) years since last abandonment of the

fallow, (d) the number of slash and burn cycles of the fallow, and (e) the slash and burn

intensity, measured as the number of years from the first slash and burn event to last

abandonment divided by the number of slash and burn cycles. Altitude and total duration

of the cultivation period were not included in the regressions due to high collinearity with

other variables. We used SYSTAT (version 10 for Windows) for the ANOVAs and

Statistica (Version 8) for the Generalized Linear Models.

We used multivariate ordination analyses to examine how species composition of herbs,

shrubs, tree seedlings, saplings, and adults varied among fallows and the secondary and

primary forests. Furthermore, we used another set of multivariate analyses in the fallows

only to assess how the measured environmental variables contributed to explaining the

variation in species composition among fallows. In order to identify species potentially

useful for restoration based on natural recruitment and survival, we used the results of the

analyses above to examine the relationship between individual species, fallow or forest

succession stage, and environmental variables. Because the abundance of tree seedlings

and shrubs was estimated both as percentage cover and counts, depending on plant size, we

used presence/absence data of these groups in the analyses. Abundance data of all other

groups of species are counts. Detrended correspondence analysis (DCA) was used to

examine the gradient length in the tree seedling, sapling, adult, shrub, and herb data

separately. Because of a relatively large gradient length for all the groups (total variation

[2.0 SD in all cases), we chose to use canonical correspondence analysis (CCA) to assess

the relationships between the environmental variables and species composition. CCA

constrained by age class as an environmental variable was used to test if there were

significant differences in species composition among age classes. For the fallows, we tested

each of the environmental variables by forward selection with all variables included and

with 999 unrestricted permutations in a Monte Carlo test. Only significant (P \ 0.05)

variables were included in the final model. All ordinations were computed by default

settings in CANOCO 4.5, and graphs produced in CanoDraw (Ter Brak and Smilauer

2002).

Results

Species richness and abundance

One-way ANOVAs showed that the species richness of tree seedlings (F5,45 = 9.02,

P \ 0.001), saplings (F5,45 = 9.81, P \ 0.001), and adults (F5,45 = 18.94, P \ 0.001) all

increased from the fallows to the secondary and primary forest, but Tukey‘s test showed

that species richness did not differ among fallows of various age for any group (Fig. 1a–c).

Tree seedling and sapling species richness did not differ significantly between secondary

and primary forest (Fig. 1a, b), whereas species richness of adult trees was significantly

higher in the primary than in the secondary forest (Fig. 1c). Species richness of shrubs did

not differ among fallows, but was significantly higher in the secondary and primary forest

(F5,45 = 9.70, P \ 0.001; Fig. 1d). Species richness of herbs decreased gradually from the

youngest fallows to the secondary and primary forest (F5,45 = 6.20, P \ 0.001; Fig. 1e).

Total species richness increased from the fallows to the secondary and primary forest

(F5,45 = 15.83, P \ 0.0001) with no differences among fallows or between secondary and

primary forest (Fig. 1f).


123

The abundance of tree seedlings increased significantly from the oldest fallows to the

secondary and primary forest (F5,45 = 5.87, P \ 0.001), with significant differences

between the three oldest fallow age-classes and the secondary forest, and between the two

oldest fallow age-classes and the primary forest (Fig. 2a). Tree saplings (F5,45 = 5.65,

P \ 0.001) and adults (F5,45 = 19.89, P \ 0.001) increased in abundance from the

youngest fallows to the secondary and primary forest, with no differences between fallows

age-classes or between the secondary and primary forests (Fig. 2b, c). The abundance of

shrubs, on the other hand, decreased from the youngest fallows to the primary forest

1-3 4-7 8-12 13-26 Sec PrimTre

e se

edlin

g sp

ecie

s ric

hnes

s (n

)

0

2

4

6

8

a aa a

b

b

Tre

e sa

plin

g sp

ecie

s ric

hnes

s (n

)

0

5

10

15

20

a a a

a

b

b

(a)A

dult

tree

spe

cies

ric

hnes

s (n

)

0

2

4

6

8

10

12

14

16

aa

aa

b

c

(b)

(c)

Shr

ub s

peci

es r

ichn

ess

(n)

2

4

6

8

10

12

14

a aa

ab

b

b

(d)

Age class

Her

b sp

ecie

s ric

hnes

s (n

)

2

4

6

8

10

12 a

abcab

abc

bc

c

(e)

Age class

Tot

al s

peci

es r

ichn

ess

(n)

10

20

30

40

50

aa a

a

b

b

(f)

1-3 4-7 8-12 13-26 Sec Prim

1-3 4-7 8-12 13-26 Sec Prim

1-3 4-7 8-12 13-26 Sec Prim1-3 4-7 8-12 13-26 Sec Prim

1-3 4-7 8-12 13-26 Sec Prim

Fig. 1 Species richness of tree seedlings (a), saplings (b), adults (c), shrubs (d), herbs (e), and total speciesrichness (f) in fallows of different age classes and secondary (Sec) and primary (Prim) forest in Vohimanaforest, Madagascar. Error bars are standard error. Bars not sharing a letter differ significantly (Tukey’s hsd,P \ 0.05)


123

(F5,45 = 4.18, P = 0.003), with a significant difference between the second age class

where shrub abundance peaked, and the older fallows, and secondary and primary forest

(Fig. 2d). Herb abundance decreased from the fallows to the secondary and primary forest

(F5,45 = 6.66, P \ 0.001), with no difference among fallow age-classes or between the two

forests types (Fig. 2e).

Generalized Linear Models multiple regressions showed that species richness and

abundance of tree seedlings, and richness of saplings, decreased with increasing number of

slash-and-burn cycles imposed to the fallows (Table 1; Fig. 3a–c). No other variables were

significantly related to seedling species richness or abundance (Table 1). The richness and

Tre

e sa

plin

g ab

unda

nce

(no

ind)

0

10

20

30

a

ab

a

abb

b

1-3 4-7 8-12 13-26 Sec Prim

Tre

e se

edlin

g ab

unda

nce

(%)

0

5

10

15

20

25

ab

ac aa

b

bc

(a)A

dult

tree

abu

ndan

ce (

no in

d)

0

5

10

15

20

25

aa

a

a

b

b

(b)

(c)

Shr

ub a

bund

ance

(no

ind)

10

20

30

40

50

60

ab

a

ab

b

b

b

(d)

Age class

Her

b ab

unda

nce

(%)

0

20

40

60

80

100 aa

aa

b

b

(e)Age class

1-3 4-7 8-12 13-26 Sec Prim

1-3 4-7 8-12 13-26 Sec Prim 1-3 4-7 8-12 13-26 Sec Prim

1-3 4-7 8-12 13-26 Sec Prim

Fig. 2 Species abundances of tree seedlings (a), saplings (b), adults (c), shrubs (d), and herbs (e) in fallowsof different age classes (1–4), secondary (5), and primary forest (6) in the Vohimana forest, Madagascar.Tree seedlings and herbs are measured as % cover, whereas all other groups are number of stems. Error barsare standard error. Bars not sharing a letter differ significantly (Tukey’s hsd, P \ 0.05)


123

Tab

le1

Gen

eral

ized

Lin

ear

Model

mult

iple

regre

ssio

ns

wit

ha

log

link

funct

ion

of

the

rela

tionsh

ips

bet

wee

nfa

llow

par

amet

ers

(pre

dic

tors

)an

dth

esp

ecie

sri

chn

ess

and

abundan

ces

of

tree

seed

lings,

sapli

ngs,

adult

s,sh

rubs,

her

bs,

and

all

spec

ies

reco

rded

inth

efa

llow

sin

Vohim

ana

fore

st,

Mad

agas

car

Pre

dic

tors

Tre

ese

edli

ng

sT

ree

sap

lin

gs

Tre

ead

ult

sS

hru

bs

Her

bs

All

spec

ies

Est

.P

Est

.P

Est

.P

Est

.P

Est

.P

Est

.P

Sp

ecie

sri

chn

ess

Dis

tan

ceto

fore

st-

0.0

00

.145

-0

.00

0.9

16

0.0

00

.185

20

.00

0.0

35

-0

.00

0.4

46

-0

.00

0.9

69

Yea

rssi

nce

aban

don

men

t0

.00

0.8

46

0.0

40

.013

0.1

0<

0.0

01

0.0

20

.01

5-

0.0

20

.21

30

.02

0.0

10

Sla

shan

db

urn

cycl

es(n

)2

0.1

00

.007

20

.06

0.0

47-

0.0

40

.445

-0

.02

0.2

28

-0

.01

0.2

13

-0

.02

0.2

03

Fal

low

du

rati

on

0.0

00

.925

-0

.07

0.0

63

-0

.19

0.0

98

0.0

10

.54

80

.02

0.2

85

-0

.00

0.8

10

Slo

pe

0.0

00

.943

0.0

00

.748

-0

.01

0.3

61

-0

.01

0.2

29

-0

.00

0.8

36

0.0

00

.818

Sp

ecie

sab

un

dan

ces

Dis

tan

ceto

fore

st-

0.0

00

.288

-0

.00

0.2

30

0.0

00

.752

20

.00

0.0

19

0.0

00

.27

0

Yea

rssi

nce

aban

don

men

t-

0.1

20

.130

0.0

60

.038

0.1

3\

0.0

012

0.9

30

.04

6-

0.0

10

.46

5

Sla

shan

db

urn

cycl

es(n

)2

0.3

90

.010

-0

.04

0.3

89

0.0

60

.040

21

.35

0.0

36

0.0

20

.05

1

Fal

low

du

rati

on

-0

.06

0.5

24

-0

.03

0.6

28

-0

.20

0.1

52

3.0

4<

0.0

01

0.0

00

.77

3

Slo

pe

-0

.03

0.0

55

0.0

10

.662

0.0

00

.844

0.5

30

.00

12

0.0

10

.01

8

Pre

dic

tor

var

iab

les,

par

amet

eres

tim

ates

(Est

.)an

dP

-val

ues

are

sho

wn

for

each

mo

del

,si

gn

ifica

nt

val

ues

(P\

0.0

5)

are

inb

old

.G

oo

dnes

so

ffi

t(s

tati

stic

s/d

.f.)&

1in

all

case

s


123

abundance of tree saplings and adults increased with the number of years since aban-

donment (Table 1; Fig. 3d–g), whereas the abundance of adult trees was positively related

to the number of slash-and-burn cycles (Table 1; Fig. 3h). Shrub species richness also

increased with years since abandonment, whereas shrub abundance slightly decreased

(Table 1; Fig. 3i, j). Shrub abundance was most strongly related to cultivation intensity,

and increased with fallow duration and decreased with number of slash-and-burn cycles

(Table 1; Fig. 3k, l). Both species richness and abundance of shrubs decreased with the

distance to the primary forest (Table 1; Fig. 3m, n), and shrub abundance increased with

the steepness of the fallow slopes (Table 1; Fig. 3o). There were no significant relation-

ships between herb species richness and any of the fallow parameters, whereas herb

abundance increased with the number of slash-and-burn cycles and decreased with the

steepness of the slope (Table 1; Fig. 3p, q). Total species richness increased with the

number of years since abandonment (Table 1; Fig. 3r).

Years since abandonment

Tre

e ad

ult a

bund

ance

Year since abandonment

Tre

e ad

ult s

p. r

ichn

ess

Slash-and-burn cycles (n)

Tre

e ad

ult a

bund

ance

(e)


Tre

e sa

plin

g ab

unda

nce

(f) (h)


Shr

ub s

p. r

ichn

ess

Distance to forest (m)

Shr

ub a

bund

ance


Shr

ub a

bund

ance

Distance to forest (m)

Shr

ub s

p. r

ichn

ess

(j) (l)

Fallow duration

Shr

ub a

bund

ance

Slope

Shr

ub a

bund

ance


Her

b ab

unda

nce

(%)


Shr

ub a

bund

ance

(p)(o)(n)

Slope

Her

b ab

unda

nce

(%)


Tot

al s

p. r

ichn

ess


Tre

e se

dlin

g ab

unda

nce


Tre

e se

dlin

g sp

. ric

hnes

s

(r)(q)

Slash-and-burn cycles (n)Tre

e sa

plin

g sp

. ric

hnes

s (c)


Tre

e sa

plin

g sp

. ric

hnes

s

(d)

(g)

(k)(i)

(m)

(b)(a)

Fig. 3 Relationships between species richness and abundances of tree seedlings, saplings, adults, shrubs,herbs, and all species recorded in the fallows in Vohimana forest, and significant (P \ 0.05) fallowparameters in GLM multiple regressions. See Table 1 for regression results


123

Species composition

Canonical correspondence analysis (CCA) showed that tree seedling species composition

changed significantly from the youngest fallows to the secondary and primary forest

(F = 2.35, P = 0.001; Fig. 4a). In the fallows, forward selection of the environmental

variables showed that the total number of slash-and-burn cycles (F = 2.37, P = 0.002)

and fallow duration (F = 1.74, P = 0.086) were the variables most related to the tree

seedling species composition (Fig. 4b). Species composition of tree saplings also changed

significantly from fallows to primary forest (F = 2.59, P = 0.001; Fig. 5a). Forward

selection showed that the number of years since abandonment was significantly related to

tree sapling species composition in the fallows (F = 1.74, P = 0.039; Fig. 5b). There was

no significant relationship between the species composition of tree seedlings or saplings

and any of the other environmental variables (F \ 1.19, P [ 0.237 in all cases). There was

no significant change in the species composition of adult trees from the youngest fallow to

the primary forest (F = 1.18, P = 0.172; Fig. 6a). In fallows, the species composition of

adult trees was significantly related to the number of slash-and-burn cycles (F = 1.04,

P = 0.014; Fig. 6b). Shrub species composition changed with the number of years since

abandonment, as shown in Fig. 7a (F = 5.37, P = 0.002). Forward selection of the

environmental variables showed that shrub species composition in the fallows were sig-

nificantly related to the number of years since abandonment (F = 3.76, P = 0.002) and the

number of slash-and-burn cycles (F = 2.18, P = 0.034), although the two most abundant

species in the fallows (Psiadia altissima and Lantana camara) appeared to be independent

of any of the environmental variables (Fig. 7b).

Potential species for restoration

The CCAs showed that some tree seedling species (Albizia chinensis, Croton mongue,Ficus baronii, Harungana madagascarensis, Tambourissa lastelliana) were associated

-0.4 1.2

-0.3

1.0

AlbiChin AnthLong

CampObtu

CrotMong

EugeBern

EugeEmir

FicuBaro HaruMada

MacaCusp

MacaUnif

OcotLeav

OmphBigl

PittVertRaveMadaTambLast

UapaThou Slash-and-burn cycles

Fallow duration(b)

-0.7 1.0

-1.0

AlbiChin

AnthLong

AnthMada

CampObtu

CrotMong

CrypHeli

CrypPerr

CrypAlseCrypThou

DalbBaro

EntaLouv

EugeBernEugeEmir

EugeHazo

EugeLagu

EugePlur

FicuBaroGambBoivGambLuci

GrewApel

HaruMada

MacaAnka

MacaCuspMacaUnif

MemeClavNoroVert

OcotCymo

OcotLeav

OcotMada

OmphBigl

PandMada

PittOcho

PittVert

PolyCoro

PotaObov

ProtDitiProtThou

RaveMada

SympTana

SympUrop

SyzyEmir

TambLast

TambAmpi

TremOrie

UapaDensUapaThouVeprMacr

VeprNiti

XyloLemu

6

5

5

5

5

2

22

3

3

4

4

4

4

6

6

6

5

5

5

5

5

5

1

1

1

1

1

2

2

2

2

3

33

3

4

(a)

1.0

Fig. 4 a CCA attribute plot of tree seedling species composition from the youngest fallows (1–4) to thesecondary (5) and primary forest (6), and b CCA biplot of tree seedling species composition andenvironmental variables selected by the forwards selection procedure in fallows in Vohimana forest,Madagascar. Full species names are shown in Table 2


123

with the youngest fallows (Fig. 4a), suggesting that these establish rapidly after aban-

donment. The presence of most of these species appeared to be independent of the envi-

ronmental factors, i.e. they occurred close to the centre of the biplot, suggesting that they

are little affected by the total number of slash-and-burn cycles or the number of years per

cycle (Fig. 4b). Most of these species, in addition to a few others, such as Trema orientalis,

also occurred as saplings in young fallows (Fig. 5a, b), and three of these species

(H. madagascarensis, C. mongue, and T. orientalis) were also associated with the fallows

as adults. None of the trees associated with the fallows as seedlings or saplings were

associated with the secondary or primary forest as adults (Fig. 6a, b), but both C. mongueand T. lastelliana occurred in the study plots.

-3 5

-10

10

AlbiChin

AlbiLebb

AnthMada

CampLepi

CampObtuCrotMongCrypPerr

EntaLouv

EugeBern

EugeEmir

FaucLaci

FicuBaro

GrewApel

HaruMadaMacar sp

OcotMada

OmphBigl

PaurLyal ProtDiti

RaveMada

SympUrop

TambLast

TambAmpi

TermOmbr

UapaDens


(b)

5-4

-2

2

AlbiChinAlbiLebb

AnthLong

AnthMada

AntiPeti

CaloChap

CampLepi

CannMada

CrotMong

CrypPerr

DombSpec

DracMada

DrypMadaEntaLouv

EvodFatr

FaucLaci

FicuBaro

FicuPyri

FiliDeci

GrewApel

HaruMada

HazoNymp

IlexMiti

MacaCusp

Macar sp

MallCapuOcotLeavOmphBigl

PandMada

PaurLyal

PittVert

PolyCoro

PotaObov

RaveMada

RavePara

TambLastTambAmpi

TambReti

TermOmbr TremOrieVeprMacr

ViteCour

XyloLemu

6

6

5

5

5

1

1

2

23

3

4

4

44

6

66

6

5

5

5

5

1

1

1

2

2

3

3

34

(a)

Fig. 5 a CCA attribute plot of tree sapling species composition from the youngest fallows (1–4) to thesecondary (5) and primary forest (6) (species[5% fit are shown), and b CCA biplot of tree sapling speciescomposition and environmental variables selected by the forwards selection procedure in fallows inVohimana forest, Madagascar. Full species names are shown in Table 2


123

Discussion

Slash-and-burn agriculture decreased plant species richness and affected species abun-

dance and composition in the Vohimana forest in Madagascar to a great extent. Even after

almost 30 years of abandonment, there was a big gap in total species richness, and richness

and abundance of seedlings, saplings and adult trees, between the oldest fallows and the

-0.5 1.0

-1.0

1.0

AnthLong

BracPerr

CampylSpp

CrotMong

CrypThou

DalbBaro

EugeBern

EugeHazo

FaucLaci

GambBoiv

GambLuci

MacaCusp

Macar sp

MamBongoNoroVertOcotCymo

ProtDiti

RaveMada

RavePara

SloaRhod

TremOrieUapaThou6

6

5

55

5

4

4

4

4

6

6

6

6

5

5

5

5 2

2

(a)

-0.4 1.2

-0.4

1.0

CrotMong

DalbBaro

EntaLouv

HaruMadaHazoNympMacaCusp

MallCapu

PandMadaPittVert

RaveMada

TremOrie Slash-and-burn cycles

UapaThou

(b)

Fig. 6 a CCA attribute plot of adult tree species composition from the youngest fallows (1–4) to thesecondary (5) and primary forest (6) (species [5% fit are shown), and b CCA biplot of adult tree speciescomposition and environmental variables selected by the forwards selection procedure in fallows inVohimana forest, Madagascar. Full species names are shown in Table 2


123

secondary and primary forest, showing that natural succession and recovery is very slow.

Our results show, however, that the duration of the recovery period may be shortened by

reducing the number of slash-and-burn cycles imposed to the area and the intensity of the

cultivation, i.e. increasing the number of years between each slash-and-burn event.

Natural succession and recovery of degraded forest ecosystems towards intact forests

depend highly on the establishment ability of tree species (Uhl 1987). One potential

limitation for the establishment of tree seedlings and saplings is the extensive invasion of

shrubs into open fallows (e.g. Styger et al. 2007), which may inhibit tree seedling growth

and survival through competition. Our results from Vohimana show that shrubs, mainly the

endemic Psiadia altissima and the non-native invasive Lantana camara, completely

dominated fallows during the first years after abandonment, with a peak of ca 50

-6 13

-10

15

AgauSali

AlloCobb

AlloMacr

AlloTric

AphlThei

BosqObov

CanthMed

DichCord DombLuci

GaerObov

LantCama

MaesLanc

MyriSpat

PachDime

PolyMaraPsiaAlti PsidCatt

PsidGuaj

PsorAndr

RubuMoll

ScheVant

SolaAuri

TambMadaTinaIson

VernCour WeinRute


Slash-and-burn cycles

(b)

-2 5

-6

8AlloDiss

AlloTric

AphlThei

CanthMed

Coffe sp

DichCord

DombLuci

ErytCori

EuphTetr

LantCama

NuxiCapi

OncoBotr

OncoElep

OncoPlat

PachDime

PandPalm

PolyMara

PsiaAlti

PsidCatt

PsycPark

RhedMada

ScheVant

SeneFauj

StreDime

TinaIson

VernAlle

VernDiss

WeinRute

6

6

55

55

5

1

122

2

2

3

33 4 4

4

44

6

6

5

55

55

5

1

4

(a)Fig. 7 a CCA attribute plot ofshrub species composition fromthe youngest fallows (1–4) to thesecondary (5) and primary forest(6), species with [5% fit to theaxes are shown, and b CCAbiplot of shrub speciescomposition and environmentalvariables selected by forwardselection in fallows in Vohimanaforest, Madagascar. Full speciesnames are shown in Table 2


123

Table 2 Full species names for abbreviations used in Figs. 4–7

Tree species Shrub species

AlbiChin Albizia chinensis AlloCobb Allophyllus cobbe

AlbiChin Albizia chinensis AlloDiss Allophylus dissectus

AlbiLebb Albizia lebbeck AlloMacr Allophyllus macrocarpus

AnthLong Anthocleista longifolia AlloTric Allophylus trichodesmus

AnthMada Anthocleista madagascariensis AphlThei Aphloia theiformis

CampObtu Campylospermum obtusifolium BosqObov Bosqueia obovata

CrotMong Croton mongue Coffe sp Coffea sp

CrypPerr Cryptocaria perrieri DichCord Dichaetanthera cordifolia

CrypThou Cryptocaria thouvenotii DombLuci Dombeya lucida

DalbBaro Dalbergia baroni ErytCori Erythoxylum corimbosum

EntaLouv Entada louvelii EuphTetr Euphorbia tetraptera

EugeBern Eugenia berneri GaerObov Gaertnera obovata

EugeEmir Eugenia emirnensis LantCama Lantana camara

EugeHazo Eugenia hazompasika MaesLanc Maesa lanceolata

EugeLagu Eugenia lagubris MyriSpat Myrica spathulata

EugePlur Eugenia pluricymosa NuxiCapi Nuxia capitata

FicuBaro Ficus baroni OncoBotr Oncostemon botryoides

GambBoiv Gambeya boivinianum OncoElep Oncostemon elephantipes

GambLuci Gambeya lucida OncoPlat Oncostemon platycladem

GrewApel Grewia apetala PachDime Pachytrophe dimepate

HaruMada Harungana madagascariensis PandPalm Pandanus palme

MacaAnka Macaranga ankafinensis PolyMara Polyscias maralia

MacaCusp Macaranga cuspidata PsiaAlti Psiadia altissima

Macar sp Macaranga sp PsidCatt Psidium cattleianum

MacaUnif Macaranga unifolia PsidGuaj Psidium guajava

MemeClav Memecylon clavistaminum PsorAndr Psorospermum androsaemifolium

NoroVert Noronhia verticillata PsycPark Psychotria parkeri

OcotCymo Ocotea cymosa RhedMada Rhedia madagascariensis

OcotLeav Ocotea leavis RubuMoll Rubus mollucanus

OcotMada Ocotea madagascariensis ScheVant Schefflera vantsilana

OmphBigl Omphalea biglandulosa SeneFauj Senecio faujasioides

PandMada Pandanus madagascariensis SolaAuri Solanum auriculatum

PittOcho Pittosporum ochosiaefolioum StreDime Streblus dimepate

PittVert Pittosporum verticulatum TambMada Tambourissa madagascariensis

PolyCoro Polyscias corolorum TinaIson Tina isonema

PotaObov Potameia obovata VernAlle Vernonia allezetei

ProtDiti Protorhus ditimena VernCour Vernonia coursii

ProtThou Protorhus thouvenotii VernDiss Vernonia dissoluta

RaveMada Ravenala madagascariensis WeinRute Weinmannia rutembergii

SympTana Symphonia tanalensis

SympUrop Symphonia urophylla

SyzyEmir Syzygium emirnense

TambLast Tambourissa lastelliana


123

individuals per 150 m2 after 4–7 years. Then, however, shrub abundance decreased, and

13–26 years after abandonment, shrub density was at the same level as for the primary

forest. Along with the decline in shrub density, species richness of shrubs and abundance of

tree seedlings and saplings increased. This shows that even if shrubs dominated during the

first stages of succession, tree species managed to establish at later stages. The estab-

lishment of tree seedlings, however, was more dependent on the total number of slash-and-

burn cycles imposed on the fallows than the number of years since the last abandonment.

This is in line with other studies showing that intensity of previous land use affect

recruitment (see Guariguata and Ostertag 2001). A higher number of slash-and-burn cycles

implicates more fire and soil disturbance, which subsequently remove more of the seed-

bank and potentially resprouting roots and stumps (Guariguata and Ostertag 2001). The

decrease in seedling species richness and abundance with increased number of slash-and-

burn cycles clearly suggests that reducing the number of slash-and-burn cycles before the

land is left to recover, may shorten the establishment period for new tree seedlings. This is

also in line with findings of Styger et al. (2007), who showed that productivity decreased

after the third slash-and-burn cycle following deforestation. To restore the soil, they

suggested an increased length of fallow periods accompanied with reduced use of fire.

Plants are not capable of utilizing all nutrients released by burning, resulting in nutrient

loss through leaching. Furthermore, fire favours aggressive exotics over native species and

herbaceous over woody species (e.g. Styger et al. 2007). The significant relationship

between slash-and-burn intensity and tree seedling species composition in our ordination

results suggests that both the total number of slash-and-burn cycles and the fallow duration

between each slash-and-burn event have an important influence on tree seedling estab-

lishment. In contrast, the richness, abundance, and composition of tree saplings depended

more on the time since abandonment than farming intensity. Thus, slash-and-burn intensity

appears to be the most critical factor for the germination and growth of tree seedlings, and

when the seedlings have established, the duration of the fallow period determines whether

they survive as saplings.

Tree planting may be another tool to speed up the slow process of natural succession,

and studies have shown that planted trees may have large effects on the recruitment of

other tree species (see Guariguata and Ostertag 2001). Moreover, by selecting the most

appropriate species for planting, both species richness and site quality can be restored

(Guariguata and Ostertag 2001). In our study, six species were associated with the fallows

as both seedlings and saplings (Albizia chinensis, Croton mongue, Ficus baronii,

Table 2 continued

Tree species Shrub species

TambAmpi Tambourissa ampifolia

TremOrie Trema orientalis

UapaDens Uapaca densifolia

UapaThou Uapaca thouarsii

UrenLoba Urena lobata

VeprMacr Vepris macrocarpa

VeprNiti Vepris nitida

XyloLemu Xylopia lemurica

ZantThou Zanthoxylum thouvenotii


123

Harungana madagascarensis, Tambourissa lastelliana, Trema orientalis), suggesting that

these species have the ability to establish fast after the fallows are left to recover and to

survive through the critical seedling phase and continue growth as saplings. Moreover,

most of these species appeared to be less dependent on the degree of previous slash-and-

burn activities. Trema orientalis and H. madagascarensis are both fast growing shade

intolerant gap species (Schatz 2001; Styger et al. 2007), suggesting that they may be good

candidates for active restoration during the first stages of the succession process. On the

other hand, H. madagascarensis may form mono-specific stands of secondary forest

(Schatz 2001) with subsequently negative effects on the establishment of other species, and

should therefore be treated with care. Albizia chinensis, F. baronii, C. mongue, and T.lastelliana are more typical forest species, although only the two latter were found within

the study forest plots. Their occurrence in the fallows suggests that these species may be

good candidates for active restoration of degraded forest ecosystems in our study area

because they have the ability both to establish rapidly after abandonment and to survive in

a dense forest. The Fabaceae A. chinensis may be suitable for active restoration because of

its N-fixing bacteria, which increase the levels of available N in the soil and thus may

facilitate growth of other species (Guariguata and Ostertag 2001; Hughes and Denslow

2005; Bristow et al. 2007). Although all these species are widespread through Madagascar,

only C. mongue is native (endemic) to Madagascar, which is crucial if the reference system

for restoration is the primary forest. Ficus baronii and H. madagascarensis are native to

central Africa, Trema orientalis and A. chinensis are both native to Asia, whereas the origin

of T. lastelliana is, as far as we know, unknown. However, we recommend all these species

to be further studied to examine their potential for restoration, i.e. if they have positive

effects on the establishment of other tree species.

We found no relationship between the distance to the primary forest and tree seedling or

sapling richness, abundance, or composition in Vohimana. This would not be a surprise if

colonizing species were specialists of disturbed habitats rather than primary forest species,

but our results show that both pioneers and forest species are among the first colonizers of

the fallows. However, mechanical deforestation might eliminate live roots and seedbanks,

but when the sites are cleared manually for cultivation without root removal, as in

Vohimana, sprouting from stumps and roots are shown to be an important source of

recruitment, in particular in the first stages of succession (e.g. Rouw 1993; Vieira and

Proctor 2007). It is, however, expected that seed dispersal from the forest will be more

important than resprout later in succession (Guariguata and Ostertag 2001). Then, a denser

canopy may also allow more shade dependent forest species to establish. Seed predation is

also an important factor in both tropical and temperate forests (see Guariguata and Ostertag

2001 and references therein), and experimental studies in cleared tropical forests in the

Amazon have shown that tree recruitment from seeds is more likely to originate from the

seed bank than from the seed rain (Uhl et al. 1982; Young et al. 1987; Lawton and Putz

1988), probably because most of the dispersed seeds are removed by animals (Uhl 1987).

Overall, our results agree with those of Mitja et al. (2008) who suggested that in fallows

following manual deforestation, with or without use of fire, pioneer and forest species

establish simultaneously and grow together in the early succession after disturbance. This

is in line with the reductionist succession model based on the Initial Floristic Composition

of Eagler (1954). The alternative holistic model, on the other hand, which predicts that

pioneer species establish first in disturbed areas, and subsequently facilitate the estab-

lishment of true forest species (Finegan 1984), may be more applicable after stronger

mechanical disturbances when removal of roots and seedbank inhibit sprouting and ger-

mination of the original vegetation (Mitja et al. 2008).


123

The slash-and-burn system is deeply rooted in traditional agricultural practice in

Madagascar, and elsewhere, and is thus likely to persist. At low yield-requirements it might

have been a sustainable system. However, with an increasing yield-requirement, primarily

due to increasing human population size, a shortening of fallow periods result in decreased

longer term yields (Styger et al. 2007). This situation causes people to extend the agri-

cultural area into primary and secondary forest. Alternatives to agricultural exploitation of

ecosystems are currently being tried in Madagascar, but these take time to establish, and

complimentary approaches are needed. Thus, increased yield of existing slash-and-burn

areas is desired in order to prevent a further degradation of existing natural forest areas.

Solutions, such as increased use of inorganic/organic fertilizer, changes to perennial crops

(e.g. banana), and planting of exotic species (e.g. Eucalyptus for fuel wood) are used in

many degraded forest ecosystems in eastern Africa, but these solutions are not optimal

because they most often create monocultures that decrease ecosystem function and bio-

diversity dramatically. Our approach is to identify species that can be used in active

restoration to speed up recovery time of fallows through species that both colonizes fallow

areas early and that occur natural in forests. This study has identified six such species that

we recommend being tested further. Seedlings can be collected from the surrounding forest

or germinated from seeds, and planted into abandoned slash-and-burn areas in order to

speed up natural succession. Transplants of seedlings have shown up to 90% survival in

tropical Amazonia, but should be planted into fallows where some vegetation is already

established, so that seedling survival is facilitated through shading (Uhl 1982, 1987).

Establishment of natural forest vegetation could result in a quicker rehabilitation and built-

up of soil nutrient stocks that make fallows usable within the needed time, such that the

extension of cultivated areas into primary forest areas is prevented, or at least reduced.

Acknowledgements We are indebted to Lesabotsy Razafindravelo, Bernard Maraina, Jean Aime Raja-onarivelo, Justin Lekamisy, and Rakoto for contributing with historical land use information and speciesidentification, Olivier Behra (MATE) for authorizing the fieldwork, the European Union 6th frameworkprogramme for funding this study through the project FOREAIM (project no. INCO-CT-2005-510790), andto two anonymous reviewers for constructive comments on a previous version of this paper.

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